1. Field of the Invention
The invention relates to a signal processing method which includes a step for constructing a sequence of images on the basis of sets of data formed from signals relating to an object comprising moving parts, said sets being periodically acquired over a given time interval. The invention also relates to an echographic device for carrying out this method. The invention is particularly useful for medical echographic imaging as a cardio-vascular diagnostic tool for non-invasive study of anomalies, such as stenoses, of arteries.
2. Description of the Related Art
A diagnostic criterion for a stenosis is an abrupt reduction of the diameter of an artery. Another criterion is the blood velocity beyond the stenosis. Studies have shown that the behavior of the blood in an artery containing stenoses does not satisfy Bernouilli's law concerning fluid flows in a sense that the flow velocity does not increase in conformity with said law in the zone in which the diameter of the artery decreases. To the contrary, the velocity of the blood flow decreases as soon as the diameter of the artery reaches a stricture threshold. Consequently, the artery gradually becomes completely occluded in the zone which is first only constricted, ultimately causing a phenomenon of thrombosis. Moreover, rigid plaques can also appear in the thickness of the walls of arteries. These plaques cause changes of the elasticity of the walls and tensions in the wall which are so large that during the cardiac cycle the arterial wall is distorted to the point of rupture and may emit emboli. Therefore, the medical field has a need for non-invasive means for studying arteries, notably injured arteries, in order to find an explanation for this behavior.
A method for the processing of echographic signals and a device for carrying out this method are already known from the published European patent application EP 0674185, which corresponds to U.S. Pat. No. 5,579,771. The known method includes the acquisition of data, at the output of an echographic system, in the form of acoustic high-frequency signals leaving a probe, the formation of an echographic image consisting of lines of pixels corresponding to the excitation lines of the probe, and the application of a temporal correlation operation to the signals, yielding velocities of displacement of structures in the echographic image.
The proposed method notably includes a step for identifying the position of an artery in a cross-sectional view, a step for calculating the radial velocity of walls of the artery along the excitation lines of the echographic probe used for forming the image, a step for calculating the amplitude of the actual movements of each wall of the artery along the excitation lines, and a step for calculating the dilatation of the artery along the excitation lines.
A technical problem resides in the fact that this data cannot be easily used so that the physician utilizing the echographic image as a diagnostic tool cannot very well profit therefrom directly.